Emissions from co-combustion of coal, wood and sludge in CFB

Paper in proceeding, 2003

This paper reports on gaseous emission from co-combustion of sewage sludge with coal or wood in circulating fluidised bed (CFB). Dried, or in some cases "wet" (mechanically dewatered), municipal sewage sludge was investigated. The fuels coal and wood were used in contrast to each other. The emissions of CO, NO, N2O, SO2 and HCl were measured from various sludge fractions and air supply methods in two CFB combustion units: the 12 MWth boiler at Chalmers University of Technology and the laboratory scale unit at the Technical University Hamburg-Harburg. The two units were scaled according to approximate scaling rules and give comparable emissions. It was shown that the emissions were moderate despite the considerable quantities of fuel nitrogen and sulphur in the sludge. For commercially interesting sludge fractions (<25 % of the energy supply) the European emission limits could be fulfilled, except in some quite extreme cases: sulphur emission from co-combustion of sludge and wood (mostly because of an odd emission rule) and for chlorine, where the emission limits are not well established. In all cases fluidized bed combustion has shown itself worthy its reputation: if the sludge handling systems are adequate, there are no further problems related to fluidization.